Advanced Iterative Synthesis of Equiripple Dual-Band Filters With Fully Prescribed Performance

Abstract

In this letter, an iterative method is presented to synthesize equiripple dual-band filters with fully prescribed in-and out-band performance. The synthesis relies on an improved Remez algorithm where respective ripple factors are introduced for the two given passbands. As a result, an equiripple response can be achieved within each passband, and their return loss (RL) (i.e., RL <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1}$</tex-math> </inline-formula> and RL <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{2})$</tex-math> </inline-formula> levels can be different and controllable by setting the ratio of the ripple factors. Note that an extra transmission zero (TZ) is thus generated and adjustable based on the RL ratio, whose location is more flexible (to prevent locating inside of a passband) when compared with previous works. To demonstrate the effectiveness of the presented method, we provide and discuss two synthetic examples with various filter functions, and obtain desired results.